Organic electroluminescent devices are attracting public attention as promising display devices for capable of emitting light of high luminance with low voltage. An important characteristic of organic electroluminescent devices is consumed electric power. Consumed electric power is represented by: (Consumed electric power=Voltage×electric current), so that the lower the value of voltage that is necessary to obtain desired brightness and the smaller the value of electric current, the lower is the consumed electric power of the device.
As one trial to lower the value of electric current that flows to a device, a light-emitting device utilizing light from ortho-metalated iridium complex (Ir(ppy)3: Tris-Ortho-Metalated Complex of Iridium(III) with 2-Phenylpyridine) is reported (e.g., refer to JP-A-2001-247859). The phosphorescent devices described therein are greatly improved in external quantum efficiency as compared with conventional singlet luminescent devices, and have succeeded in making the value of electric current smaller.
For the purpose of improving the efficiency and durability of a phosphorescent device, a device containing an indole derivative (JP-A-2002-305084) and a device containing a platinum complex (WO 04/108857) are reported. However, in view of durability and efficiency, an improvement is required of these techniques. In addition, a further betterment in tint variation by aging is desired.